"True, I also included them in my metal list. For some of these the lines were pretty blurred."

Yeah a lot of those harder/heavier alternative bands like Alice In Chains, Deftones, Tool, Melvins, Kyuss...they kinda operate in a grey area where it's difficult to say whether they're metal or aren't (and at their heaviest they also feel too heavy to be just called "rock"). Personally, the albums I own by those bands I just have them grouped in my metal collection